Toxic minerals

Toxic minerals are those minerals that present a certain risk to public health. Among these minerals are asbestos and silica. In addition, other minerals contain toxic metals such as mercury and lead. The most common diseases caused by toxic minerals are cancer and neurological disorders. The toxic effects of some minerals, such as lead or mercury, can be irreversible if left untreated.

Toxic Minerals and Their Use

Toxic minerals are minerals that are hazardous to human health. A mineral by itself, or its components, can be toxic. Typical examples of the former are asbestos, selenium, and silica minerals; typical examples of the latter are minerals containing such toxic chemicals as arsenic, lead, mercury, or cadmium.

Six fibrous silicate minerals are defined as asbestos: crocidolite, amosite, chrysotile, tremolite, actinolite, and anthophyllite. The most hazardous of the asbestos minerals are crocidolite and amosite. The best known in the United States is chrysotile, a magnesium silicate.

Asbestos, an excellent insulator, was widely used in construction beginning in the nineteenth century; it has since been banned in Europe and is regulated in the United States. Before the discovery of asbestos’s toxicity, it was a common component of drywall, fire blankets, fireproof clothing for firefighters, thermal pipe insulation, and gas mask filters.

The toxicity of other minerals such as talc and vermiculite is related to asbestos contamination.

Talc is a magnesium silicate mineral with the chemical formula Mg₃Si₄O₁₀(OH)₂. It is widely used in a form of talcum powder for preventing diaper rash and in surgical gloves.

Vermiculite is a mineral from the group of mica (sheet) minerals with approximate chemical formula Mg⁺², Fe⁺², Fe⁺³)₃ [(AlSi)₄O₁₀]·(OH)₂·4H₂O. It was widely used in construction for fire protection and for the insulation of pipes and roofs. In the United States alone, about 35 million homes contain vermiculite.

Other potentially hazardous minerals are silica and selenium. Silica, or silicon dioxide (chemical formula SiO₂), can be found in nature as mineral quartz or sand. Silica is a common food additive. For example, table salt contains silica. Silica also is a primary component of diatomaceous earth, which is used as a filter aid, commonly in backyard pools. According to the Centers for Disease Control and Prevention, nearly 1.7 million workers in the United States are exposed to silica in a variety of industries and occupations, including in construction and mining.

Selenium is both a chemical element and a mineral. This mineral is mainly used to manufacture glass, making it green or red. Selenium also is used in the electronics industry.

Several minerals contain such toxic metals as lead, mercury, cadmium, chromium, and arsenic. These metals, also called heavy metals, are poisonous. The main mineral containing lead is galena (PbS), which is up to 86.6 percent lead. Other common lead minerals are cerrusite (PbCO₃) and anglesite (PbSO₄). Lead, which can be easily extracted from its minerals, was known to ancient Egyptians and Babylonians and is mentioned in the Bible. Since Roman times, people have used lead for plumbing and as a food and drink preservative. During the Middle Ages, lead was used for roofing.

The major use of lead today is for batteries. Lead also is used as a protective shield against radiation. One lead mineral that was historically used as a natural dye is chrome yellow, which is toxic. Chrome yellow is a natural yellow pigment made of lead chromate (PbCrO4).

Cinnabar (HgS) is the most common mineral of mercury. It has been known for some time and has been an object of fascination because of its appearance. Mercury was used since Roman times as a natural dye. Dentists use it today to make amalgams to fill cavities, although not without controversy.

Several rare minerals contain the metal cadmium. Cadmium is used in industry for making some types of paints and batteries and in electroplating. Chromium is mined as chromite (FeCr₂O₄). It is used in metallurgy; stainless steel usually contains chromium. Chromium also is used as a paint pigment (school buses are painted in chrome yellow) and for tanning leather (such as for sofas).

Another heavy metal is arsenic, which is not exactly a metal but has several metallic properties. Arsenic occurs in many minerals. The most common arsenic minerals are realgar, orpiment, and arsenopyrite, which are frequently sources of arsenic in industry. Realgar is known as the ruby of arsenic and was used in ancient Rome as a red paint pigment. It is now used occasionally for killing weeds, insects, and rodents. Orpiment also was used as a pigment in painting in ancient times. However, it also was used in poison arrows, as its toxic nature was well known.

There also exist minerals of lower toxicity and minerals with inconclusive evidence of toxicity; these include aluminum, tin, and zinc. Most common aluminum minerals are feldspars. They are aluminosilicates and make up to 60 percent of the earth’s crust, or the rock shell that surrounds the planet. There also exist other aluminum minerals, such as beryl (Be₃Al₂Si₆O₁₈), cryolite (Na₃AlF₆), and corundum (Al₂O₃). Aluminum is widely used in the airplane and electronics industries and for making foil (wrapping material) and cooking pans.

The Health Hazard of Toxic Chemicals

All toxic minerals are hazardous to humans. The effect of toxic chemicals on human health can be immediate (acute) or can occur through years (chronic).

Most common diseases caused by toxic minerals are cancer and neurological disorders. Toxic minerals act as carcinogens, chemicals that alter genetic mechanisms. Experts have not determined how toxic minerals cause cancer.

Asbestos causes several serious illnesses, including asbestosis, lung cancer, and mesothelioma. Inhalation of asbestos fibers causes asbestosis (pulmonary fibrosis) within a short time. Asbestosis is the formation of scar tissue (fibrosis) inside the lungs. Symptoms include chest pain, tightness in the chest, cough, and shortness of breath that worsens with time. Asbestos also can cause cancer, especially lung cancer or mesothelioma. Mesothelioma is a rare cancer of the lining of body cavities.

The majority of asbestos-related cancers are caused by the asbestos mineral crocidolite. In the past, before crocidolite mines were closed, about 18 percent of crocidolite miners died from cancer. Chrysotile is more common but appears less dangerous. Both talc and vermiculite minerals, which contain asbestos, also cause cancers, especially of the lung.

The most common disease caused by exposure to silica is silicosis. Other diseases are lung cancer, autoimmune disorders, and chronic renal disease. Silicosis is a disease marked by inflammation and lesions in the lungs. Selenium can cause selenosis if taken in excessive amounts. Symptoms of this disease include hair loss, gastrointestinal disorders, fatigue, irritability, and nervous system damage.

Heavy metals primarily inhibit the functioning of important enzymes in the human body. Many enzymes have sulfhydryl groups. Heavy metals attach to these groups, making enzymes inactive.

The toxicity of lead and lead mineral (galena) has been known since ancient times. Humans used galena to obtain metallic lead. Minerals containing lead are toxic to many tissues and organs, including the heart, bones, intestines, kidneys, brain, and reproductive system. Also, lead ions inhibit enzymes necessary for the synthesis of hemoglobin (the oxygen carrier in human blood). Lead poisoning causes mental retardation and neurological disorders. This damage can be irreversible if untreated. Historically, lead poisoning was a major problem in children, particularly those who lived in old homes.

Lead poisoning is treated with calcium salt of ethylenediaminetetraacetatic acid (EDTA), with the lead-catching, chelating agent (from the Greek chela meaning “claw”) being administered intravenously. In the human body, calcium ions of EDTA are replaced by lead.

Mercury toxicity is notorious, but pure metallic mercury is not particularly hazardous. Ingestion of small amounts of mercury from dental fillings will not produce any health problems. Mercury compounds, however, are dangerous. Mineral cinnabar is extremely toxic by ingestion. The mining of cinnabar in ancient times was regarded as a death sentence. The exposure to cinnabar can result in damage to the brain, kidney, and lungs; birth defects; and several other diseases, including insanity. Damaging effects are usually irreversible. As in the case of lead, antidotes exist for mercury poisoning and include chelating agents such as British anti-lewisite (BAL). Mercury ions can attach to it and be deactivated (prevented from attacking body systems).

Various other minerals containing heavy metals are extremely toxic to humans. These other minerals include those containing cadmium and chromium. Poisoning with cadmium leads to loss of calcium ions (Ca⁺) from bones, making them fragile and easy to break. Cadmium poisoning also causes pain, vomiting, and diarrhea. The toxicity and carcinogenic properties of chromium are known as well. Chromium minerals also can cause allergic reactions in some people.

Arsenic mineral poisoning causes headaches, confusion, severe diarrhea, and drowsiness and usually affects the lungs, skin, kidneys, and liver. The final result of arsenic poisoning is death. Arsenic poisoning was one of the favorite methods for murder in the Middle Ages. Because of its slow effect, arsenic poisoning often went undetected. Today, arsenic poisoning is a global problem because of its natural contamination of groundwaters. Chelating agents are used to treat arsenic poisoning.

Compared with other toxic minerals and their components, is not extremely toxic. Data on its low toxicity appeared only recently. Some toxicity of aluminum is related to its deposition in bones, where it replaces calcium, contributing to reduced hardness of bones and, when occurring in infants, growth retardation. There also is some inconclusive evidence that aluminum exposure increases the risk of breast cancer and some brain diseases, such as Alzheimer’s desease.

Management of Toxic Minerals

Humans have been mining toxic minerals for thousands of years and have been poisoned by these minerals in the process. Several U.S. government agencies, including the Environmental Protection Agency (EPA) and the National Toxicology Program, have data on toxic minerals that are available to the public, health practitioners, scientists, and industry workers.

The EPA requires that containers and vehicles in which toxic minerals are stored or carried display signs identifying the hazard. Public fears of developing cancer from toxic minerals have led to regulations that request the minerals’ removal from public and private places.

Scientists normally conduct tests on animals to identify toxic effects and hazardous doses (the level of exposure and the amount of toxic mineral). For example, LDL₀ (the lowest dose at which animal death occurs) for aluminum is 6207 mg per kilogram (a low toxicity chemical) compared with arsenic of 70 mg/kg (a high toxicity chemical). Humans are able to deal with low doses of toxic minerals.

The level in which toxic effects are not observed is the threshold level. Higher levels of toxic minerals can also be tolerated if the time of exposure is short. Toxicologists normally know the threshold level of acute diseases caused by minerals. Scientists, however, do not know the threshold level of toxic minerals for cancer.

Principal Terms

aluminum: the most abundant metal in the earth’s crust

arsenic: a chemical element with a metallic appearance

cadmium: a soft element

chromium: a lustrous hard metal

LD50: in toxicology, the abbreviation for the lethal dose for 50 percent of test animals; lethal dose is expressed in milligrams of poison per unit body weight of the animal

lead: a soft metal

mercury: the only liquid metal at room temperature

mineral: a solid, inorganic natural substance with a distinct chemical composition and a specific crystalline structure; minerals are formed by geologic processes

selenium: an element of the sulfur family; several forms of selenium are known, including a metallic selenium

toxicology: the study of the effects of toxic compounds on humans and environments

Bibliography

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